The use of a motor-driven concave friction drive wheel as an auxiliary drive unit for a bicycle is well known. The pedal system is the primary system with an electric direct current (dc) motor power source (U.S. Pat. No. 627,066) or a gas-driven power source (U.S. Pat. No. 633,484) mounted to the frame structure of the bicycle. The concave drive wheel of U.S. Pat. No. 1,158,311 is mounted to an engine drive shaft and a spring tension member is used to maintain a positive drive contact with a rear tire tread surface.
U.S. Pat. Nos. 1,436,788; 2,578,886; 3,431,994; and 4,974,695 each discloses a concave friction drive wheel that engages the tire tread surface to provide a power assist to a bicycle or a similar vehicle. U.S. Pat. No. 1,436,788 more specifically discloses two concave wheels for frictionally driving the rear wheel of a bicycle using a single electrically powered drive motor. The concave drive wheel of U.S. Pat. No. 4,974,695 is designed to engage as large an area of the motorcycle tire as possible for driving it in reverse without the use of the motorcycle engine or transmission structure.
U.S. Pat. Nos. 2,451,965 and 2,493,275 disclose a pair of drive wheels in systems for frictionally contacting the tread surface of a bicycle tire. In each instance, however, the pair of drive wheels is used with either a belt or only one of the drive wheels is in direct contact with the tire during operation. U.S. Pat. No. 2,578,886; 3,431,994; and 4,974,695 each discloses a concave shaped drive wheel for various frictional drive systems. None of these prior systems, however, disclose a dual concave drive system like that of this invention.
The following patents disclose different drive roller configurations and surface styles (smooth and roughened) for wheels that frictionally drive the balloon tire of the vehicle wheel being driven. 2,409,887 4,227,589 5,069,304 5,078,227 5,316,101
U.S. Pat. Nos. 1,409,454 and 1,442,556 show mechanisms that act directly on the bicycle tire being driven. As shown, an electric dc motor with a battery power supply is well known for use with a drive system of the invention. While various components of the invention are shown in the prior art, none of the references shows the specific structural configuration of drive roller assembly of the invention.
U.S. Pat. No. 5,078,227 discloses a retrofit device that provides an auxiliary electrical drive mechanism for vehicles such as bicycles and wheelchairs. The system includes first and second electric motors each used with a friction drive element and apparatus for selectively bringing the friction drive elements into operative driving engagement with both the rim and tire of the vehicle wheel to effect a frictional driving function. More specifically, each of the electric motors are pivotally mounted about a single pivot point whereby the first and second motors can maintain a driving engagement with the vehicle wheel regardless of the eccentricities of the wheel. Unlike the invention, this known system does not contact the tread portion to drive the wheel.
U.S. Pat. No. 5,316,101 discloses an electric propulsion system for a multi-wheeled vehicle using a solar charging mechanism. The standard components of a typical electric bicycle include a bicycle, a conventional battery, a dc electric motor, drive means for mechanically connecting the motor with a vehicle wheel, and a means for electrically connecting the battery to the motor for rotating the drive wheel when it is in frictional contact with the vehicle wheel. It is known for a pedal and motor power to function in combination to add range between recharges of the battery and improve speed and hill climbing ability. As in the invention, some known regenerative braking systems include a motor that acts as a generator when slowing or stopping to convert the forward momentum of the bicycle and rider into a charging current to restore energy to the battery.
U.S. Pat. No. 5,603,388 discloses a pair of drive rollers which act on opposing sides of the vehicle wheel to effect the desired power assist.
U.S. Pat. Nos. 5,491,390 and 5,671,821 disclose an electric propulsion system for a bicycle having a battery-powered drive roller that is designed to operate with any type of the tread surface using a cylindrically-shaped drive member.
U.S. Pat. No. 3,978,936 discloses a retrofit system having a means for selectively engaging the drive wheel with the vehicle wheel. U.S. Pat. Nos. 3,841,428; 3,961,678; 4,579,188; and 5,078,227 disclose various auxiliary attachments for a multi-wheeled vehicle. U.S. Pat. No. 3,961,678 particularly shows a frame member mounted to a rear wheel frame structure to mount the drive wheel mechanism above the vehicle wheel.
U.S. Pat. No. 5,513,721 discloses a particular cover structure and battery storing case for an electric-powered vehicle. U.S. Pat. Nos. 4,637,274; 5,662,187; and 5,704,441 disclose various types of drive mechanisms designed for operating within the vehicle pedal mechanism to assist the driver.
Most of the known systems perform poorly on wet tire surfaces and require relatively smooth tire tread to maintain drive friction.